Cannot reach server through my DSL, only through 3G. Why?

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Cannot reach server through my DSL, only through 3G. Why?

Postposted on Wed May 02, 2012 10:10 pm

Hi. I am a freelance web designer. I live in Brazil but work for clients in Sweden. Now I am suddenly having problems accessing the e-mail server of a client, a server which I have been accessing without problems for several years. The connection times out when I try to access the server through my DSL. If I connect my phone to my computer and enable a 3G connection I can access the server normally.

After five days of this I am starting to believe that my problems will not go away by themselves. I am guessing that for some reason my connection attempts are being filtered and discarded somewhere. There are lots of hacker attacks originating from Brazil from what I've understood, and maybe some overzealous filtering somewhere is making life hard for me. Maybe they are blocking parts of the IP range of my ISP or something. Or it may be something else, I'm no network expert.

But I know that some people on these forums are, so maybe someone can help me figure out what's going on and who I should contact about it. I ran some traceroutes (I have redacted the destination IP and server name, I guess they're not important).


-- THROUGH DSL ------------------------

C:\Users\Jan>tracert XXX.XXX.se

Tracing route to XXX.XXX.se [212.247.XXX.XXX]
over a maximum of 30 hops:

1 1 ms 1 ms 1 ms 192.168.1.1
2 * * * Request timed out.
3 39 ms 38 ms 38 ms 201-0-91-17.dsl.telesp.net.br [201.0.91.17]
4 41 ms 41 ms 41 ms 201-0-5-73.dsl.telesp.net.br [201.0.5.73]
5 47 ms 41 ms 47 ms 187-100-57-81.dsl.telesp.net.br [187.100.57.81]
6 43 ms 44 ms 42 ms Xe3-1-0-0-grtsanem2.red.telefonica-wholesale.net.10.16.84.in-addr.arpa [84.16.10.17]
7 152 ms 207 ms 245 ms Xe-6-1-0-0-grtmiabr3.red.telefonica-wholesale.net [94.142.124.170]
8 196 ms 187 ms 190 ms Xe2-0-0-0-grtwaseq5.red.telefonica-wholesale.net [84.16.14.201]
9 200 ms 180 ms 176 ms sl-st31-ash-.sprintlink.net [144.228.205.29]
10 * * * Request timed out.
11 * * * Request timed out.
12 * * * Request timed out.

... (they all time out until 30 tries)



-- THROUGH MOBILE CONNECTION -----------------

C:\Users\Jan>tracert XXX.XXX.se

Tracing route to XXX.XXX.se [212.247.XXX.XXX]
over a maximum of 30 hops:

1 * * * Request timed out.
2 134 ms 139 ms 131 ms 10.90.35.84
3 133 ms 83 ms 92 ms 200.142.133.125
4 451 ms 407 ms 306 ms 200.142.132.2
5 95 ms 93 ms 108 ms 200.142.132.1
6 83 ms 81 ms 107 ms 187-100-62-113.dsl.telesp.net.br [187.100.62.113]
7 91 ms 87 ms 78 ms 201-0-5-185.dsl.telesp.net.br [201.0.5.185]
8 2276 ms 938 ms 320 ms Xe3-1-0-0-grtsanem2.red.telefonica-wholesale.net.10.16.84.in-addr.arpa [84.16.10.17]
9 205 ms 266 ms 236 ms Xe12-0-4-0-grtmiabr4.red.telefonica-wholesale.net.117.142.94.in-addr.arpa [94.142.117.42]
10 297 ms 241 ms 280 ms Xe2-0-0-0-grtwaseq5.red.telefonica-wholesale.net [84.16.14.201]
11 230 ms 239 ms 235 ms sl-st31-ash-.sprintlink.net [144.228.205.29]
12 245 ms 237 ms 257 ms sl-tele22-363835-0.sprintlink.net [144.228.205.66]
13 280 ms 1125 ms 463 ms nyc9-core-1.pos1-0-0.tele2.net [130.244.207.217]
14 500 ms 459 ms 521 ms ams-core-1.pos0-7-3-0.tele2.net [130.244.218.213]
15 1125 ms 408 ms 374 ms gbg-core-2.bundle-pos1.tele2.net [130.244.205.149]
16 332 ms 316 ms 534 ms gbg-pe-1.tengigabiteth1-1.tele2.net [130.244.52.86]
17 383 ms 359 ms 344 ms XXX.XXX.XXX.se [212.247.XXX.XXX]

Trace complete.



Both calls pass through the same servers in the middle, but when on DSL no server after sl-st31-ash-.sprintlink.net replies. I guess that's where my connection attempt is filtered out. Or could it be something else entirely? Should I contact my ISP about this, or is there something else I should try first?

Thankful for any insights.
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Re: Cannot reach server through my DSL, only through 3G. Why

Postposted on Thu May 03, 2012 7:34 am

Your initial diagnosis may be correct -- your connection may be filtered/blocked based on source IP. It is also possible that there is a misconfigured router causing the reply packets to get lost.

Are you able to access other servers (e.g. web) at your client normally, or is the e-mail server the only one you use? (Or is the e-mail server a webmail server?)

Can you have someone at your client's office try pinging/tracerouting you (both on your DSL and your mobile connection)? That might give us some additional clues.

Have you filed a trouble report with your ISP?

If it is not resolved soon, and accessing it via your mobile connection isn't a viable long-term workaround, you could try using a proxy to access the problematic server. If you know anyone outside of Brazil who has a Linux/UNIX system they'd be willing to give you an account on, you can easily use that as a SOCKS proxy to make the connection appear that it is coming from the proxy system instead of Brazil.
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Re: Cannot reach server through my DSL, only through 3G. Why

Postposted on Thu May 03, 2012 7:49 am

Thanks for your input and suggestions. Of course, when I woke up this morning everything was back to normal. Guess it might have been a malfunctioning router or badly configured filter that was finally fixed. I will keep your advice in mind and take the steps you suggested if/when it happens again.

Once again, thanks for your time and effort.
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